The invention relates generally to x-ray tubes and, more particularly, to a high emissive coating on a target face and/or a target shaft of an x-ray tube.
X-ray systems typically include an x-ray tube, a detector, and a bearing assembly to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then transmits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in a computed tomography (CT) package scanner.
X-ray tubes include an anode structure comprising a target onto which the electron beam impinges and from which x-rays are generated. An x-ray tube cathode provides a focused electron beam that is accelerated across a cathode-to-anode vacuum gap and produces x-rays upon impact with the anode target. Because of the high temperatures generated when the electron beam strikes the target, the anode assembly is typically rotated at high rotational speed for the purpose of distributing heat generated at a focal spot. The anode is typically rotated by an induction motor having a cylindrical rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. The rotor of the rotating anode assembly is driven by the stator.
Newer generation x-ray tubes have increasing demands for providing higher peak power. Higher peak power, though, results in higher peak temperatures occurring in the target assembly, particularly at the target “track,” or the point of electron beam impact on the target. Thus, for increased peak power applied, there are life and reliability issues with respect to the target.
Emissive coatings may be applied to x-ray tube targets in order to enhance radiative heat transfer and reduce the operating temperature of the components therein, such as the target and the bearing assembly. However, such coatings are typically based on oxides, such as mixtures of ZrO2—TiO2—Al2O3, which tend be unstable and outgas at, for instance, 1200° C. or greater. Typically, the outgas includes carbon monoxide (CO), which results from poor chemical stability of oxide constituents (e.g., TiO2) with the reducing components of the target substrate (e.g., Mo2C phase in TZM-Mo) at its operating temperature. CO and other outgas products compromise the high-vacuum environment of the x-ray tube, making such reaction products undesirable.
Therefore, it would be desirable to have a method and apparatus to improve thermal performance and reliability of an x-ray tube target and bearing while reducing outgas emissions.